Method of determining a clearance

ABSTRACT

A method of determining timing clearance between a valve stem and a moving member using an electromagnetic actuator comprising electromagnets, an electromagnet for moving the moving member from a closed position towards an open position and an electromagnet for moving the moving member from an open position towards a closed position, each electromagnet being controlled on the basis of a reference electrical characteristic, the method comprising: controlling an electromagnet to obtain a displacement speed for a moving member as the moving member moves from one of a closed position or an open position towards the other one of an open position or a closed position; obtaining values of a reference electrical characteristic for intermediate positions of the moving member; and detecting an intermediate position at which the reference electrical characteristic is subject to a sudden change.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of application PCT/FR03/02170,filed Jul. 10, 2003, and claims priority to French patent application 0209434 filed Jul. 25, 2002, the disclosures of which are incorporatedherein by reference in their entirety.

FIELD

The present invention relates to a method of determining timingclearance between two moving parts.

BACKGROUND

Conventional electromagnetic valve actuators comprise both resilientdisplacement means and electromagnetic actuator means for actuating themoving member between two extreme positions which correspondrespectively to the open position of the valve and to the closedposition of the valve. The resilient displacement means generallycomprise a spring associated with the moving member to return itelastically into its extreme open position, and a spring associated withthe valve stem in order to return it elastically into its closedposition so as to urge the moving member elastically into its extremeclosed position. The electromagnetic actuator means generally comprisean electromagnetic displacement means for bringing and/or holding themoving member in its extreme open position, and an electromagnet forbringing and/or holding the moving member in its extreme closedposition.

In order to be certain that the valve is properly pressed against itsseat when the moving member is in its extreme closed position andtherefore the moving member and the valve are not connected to eachother, timing clearance is provided between the moving member and thevalve stem when the moving member is in its extreme closed position andthe valve is properly pressed against its seat by the spring which isassociated therewith.

Under such circumstances, if the moving member is brought quickly fromthe extreme closed position to the extreme open position, the movingmember will strike the valve stem. This impact, which in any event isnoisy, leads to mechanical stresses and wear of the moving member and ofthe valve stem that can, in extreme cases, lead to damage thereof. It istherefore important to know precisely the amount of timing clearancethat exists so that the electromagnetic means can be controlled firstlyto bring the moving member gently into contact with the valve stem, andthen to accelerate the moving member once it is pressing against thevalve stem.

Unfortunately, timing clearance varies while the engine is in operation,in particular as a function of temperature, and also over the lifetimeof the engine, in particular as a function of the wear of the valve andof the various components of the valve actuator. In addition, timingclearance can vary from one valve actuator to another as a function oftheir manufacturing tolerances.

In order to determine the timing clearance, a conventional methodcomprises controlling the valve actuator means to move the moving memberfrom the extreme closed position to the extreme open position and todetect variation in an electrical characteristic of the electromagneticactuator means. This variation in the electrical characteristic iscaused by the increase in the opposition to movement of the movingmember once it encounters the valve stem. The timing clearance is thendetermined by measuring the time that elapses between the beginning ofthe moving member being set into motion and the start of variation inthe electrical characteristic. Nevertheless, determining timingclearance in that way turns out to be relatively inaccurate. Thus, thereis a need for a method of determining timing clearance simply andaccurately.

SUMMARY

A first embodiment of the invention is a method of determining timingclearance between a valve stem and a moving member using anelectromagnetic actuator comprising electromagnetic displacement meanswhich comprise electromagnets for moving the moving member between anextreme closed position and an extreme open position, the electromagnetsof the electromagnetic displacement means being controlled byservo-control means on the basis of a reference electricalcharacteristic. The method comprising: controlling the electromagneticdisplacement means to obtain a substantially constant displacement speedfor the moving member as the moving member moves between the extremeclosed position and the extreme open position; obtaining values of thereference electrical characteristic for intermediate positions of themoving member; and detecting an intermediate position at which thereference electrical characteristic is subject to a sudden change. Themethod can further comprise deducing the timing clearance from theintermediate position at which the reference electrical characteristicis subject to a sudden change and the extreme closed position.

One advantage of the method is that it is a simple, yet accurate methodfor determining timing clearance. A further advantage of the method isthat it can be used to determine the timing clearance in a machine whilethe machine is in operation in its normal state or in an idle statesince the implementation of the method does not interfere with normaloperation of the machine and does not generate additional noise.

A second embodiment of the invention is a method of determining timingclearance between a valve stem and a moving member using anelectromagnetic actuator comprising electromagnets, an electromagnet formoving the moving member from a closed position towards an open positionand an electromagnet for moving the moving member from an open positiontowards a closed position, each electromagnet being controlled on thebasis of a reference electrical characteristic. The method comprises:controlling an electromagnet to obtain a displacement speed for a movingmember as the moving member moves from one of a closed position or anopen position towards the other one of an open position or a closedposition; obtaining values of a reference electrical characteristic forintermediate positions of the moving member; and detecting anintermediate position at which the reference electrical characteristicis subject to a sudden change. The method can further comprise deducingthe timing clearance from the intermediate position at which thereference electrical characteristic is subject to a sudden change andthe open position, when the moving member moves towards the closedposition, and the closed position, when the moving member moves towardsthe open position.

Other embodiments of the invention which give rise to noisier operationof the actuator are also envisaged. One advantage of these otherembodiment is that they can be used when the machine in which theembodiments take place is starting or when the machine is operating at aspeed greater than some predetermined speed, such as 2000 revolutionsper minute (rpm).

These and other objects, advantages and features of embodiments of theinvention, together with the organization and manner of operationthereof, will become apparent from the following detailed descriptionwhen taken in conjunction with the accompanying drawing, wherein likeelements have like numerals throughout the drawing described below.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an illustration of a mechanical device comprising a valve anda moving member which can be actuated to perform a method of determiningtiming clearance according to embodiments of the present invention.

DETAILED DESCRIPTION

As used herein, the term “timing clearance” means the distance between afirst point defined as the point at which the moving member 8 is setinto motion and a second point defined as the point at which the movingmember is located at the start of variation in the reference electricalcharacteristic.

A first embodiment of the invention is a method of determining timingclearance between a valve stem 3 and a moving member 8 using anelectromagnetic actuator comprising electromagnetic displacement meanswhich comprise electromagnets 14 and 15 for moving the moving member 8between an extreme closed position and an extreme open position, theelectromagnets 14 and 15 of the electromagnetic displacement means beingcontrolled by servo-control means on the basis of a reference electricalcharacteristic. The method comprises: controlling the electromagneticdisplacement means to obtain a substantially constant displacement speedfor the moving member 8 as the moving member 8 moves between the extremeclosed position and the extreme open position; obtaining values of thereference electrical characteristic for intermediate positions of themoving member; and detecting an intermediate position at which thereference electrical characteristic is subject to a sudden change. Themethod can further comprise deducing the timing clearance from theintermediate position at which the reference electrical characteristicis subject to a sudden change and the extreme closed position.

A second embodiment of the invention is a method of determining timingclearance between a valve stem 3 and a moving member 8 using anelectromagnetic actuator which comprises electromagnets 14 and 15, anelectromagnet 15 for moving the moving member 8 from a closed positiontowards an open position and an electromagnet 14 for moving the movingmember 8 from an open position towards a closed position, eachelectromagnet being controlled on the basis of a reference electricalcharacteristic. The electromagnets 14 and 15 can be controlled by aservo-controller. The method comprises: controlling an electromagnet 14or 15 to obtain a displacement speed for a moving member 8 as the movingmember 8 moves from one of a closed position or an open position towardsthe other one of an open position or a closed position; obtaining valuesof a reference electrical characteristic for intermediate positions ofthe moving member 8; and detecting an intermediate position at which thereference electrical characteristic is subject to a sudden change. Themethod can further comprise deducing the timing clearance from theintermediate position at which the reference electrical characteristicis subject to a sudden change and the open position, when the movingmember 8 moves towards the closed position, and the closed position,when the moving member 8 moves towards the open position. Under suchcircumstances, the displacement speed of the moving member 8 can bemaintained at a substantially constant speed from, for example, a middleintermediate position of the armature 12.

The embodiments of the invention can be used in engines 2 comprisingvalves 1 each valve 1 associated with a respective actuator 6. Theembodiments serve to determine the timing clearance that exists betweeneach valve stem 3 and the moving member 8 of the actuator 6 thatcooperates with the valve stem 3 in order to move the valve 1 between anopen position in which the valve 1 is spaced apart from its seat 5, andan extreme closed position in which the valve 1 is properly pressedagainst its seat 5.

The embodiments of the invention are described with reference to FIG. 1.A valve 1 is comprised of a valve stem 3 which is mounted in a cylinderhead 4. The cylinder head 4 can be located inside of any suitablemechanical device, including, but not limited to, an engine. The valve 1is located at some point between an extreme closed position, in whichthe valve 1 is properly pressed against a seat 5 of the cylinder head 4,and an open position, in which the valve 1 is separated from the seat 5of the cylinder head 4.

Between the extreme closed position and the open position, the valve 1is actuated by means of an actuator 6 which is mounted on the cylinderhead 4 of a suitable mechanical device. FIG. 1 depicts an engine 2 as anexemplary mechanical device in which the embodiments can operate. Theactuator can be mounted on other locations within an engine or othersuitable mechanical device as well.

The actuator 6 comprises a body 7 having a moving member 8 slidablymounted therein. The moving member 8 comprises a rod 9 with a first end10 arranged to bear against a free end of the valve stem 3, and a secondend 11 secured to an armature 12 received in a housing 13 of the body 7to slide parallel to the rod 9.

The body 7 comprises electromagnetic displacement means for moving themoving member 8. The electromagnetic displacement means can comprise anelectromagnet 14 for holding the armature 12 in an extreme closedposition of the valve 1, and an electromagnet 15 for holding thearmature 12 in an open position of the valve 1, wherein theelectromagnets are open to two opposite faces of the housing 13 of thebody 7. In this case, the armature 12 comes into contact with theelectromagnet 14 when it is in the extreme closed position and thearmature 12 comes into contact with the electromagnet 15 when it is inthe extreme open position.

The electromagnets 14 and 15 can be servo-controlled by means (notshown) from a reference electrical characteristic and from adisplacement speed of the moving member 8. The method of servo-controlof devices such as electromagnets is known to one of ordinary skill inthe art. Such servo-control in an engine, for example, can be performedby an engine controller unit which makes use of a signal representativeof the speed of the armature 12 and obtained by computing the derivativeof a position signal supplied by a sensor 16 for sensing the position ofthe rod 9. The sensor 16 can be any number of types of sensors,including, but not limited to, a conventional Hall effect sensor.

The displacement speed of the moving member 8 can be kept substantiallyconstant while the moving member 8 moves from an closed position towardsan open position, or at least while the moving member 8 is moving over adistance that is greater than the maximum possible timing clearance,given the geometrical characteristics of the actuator 6, the valve 1 andthe cylinder head 4.

The reference electrical characteristic can include, but is not limitedto, a reference current or a reference voltage.

In a manner known to one of ordinary skill in the art, the actuator 6includes a resilient displacement means.

The resilient displacement means comprise a spring 17 interposed betweena face 18 of the body 7 and a shoulder 19 of the rod 9 to urge thearmature 12 towards the extreme open position, and a spring 20interposed between a face 21 of the cylinder head 4 and a shoulder 22 onthe valve stem 3 in order to urge the valve 1 into the closed position.

The actuator 6, the cylinder head 4, and the valve 1 are arranged insuch a manner that when the armature 12 is in the extreme closedposition and the valve 1 is pressed against its seat 5, there existstiming clearance j between the first end 10 of the rod 9 and the freeend of the valve stem 3.

Reference electrical characteristic values for intermediate positions ofthe moving member 8 during movement of the moving member 8 from a closedposition towards an open position or from an open position towards aclosed position can be obtained by a number of methods, including, butnot limited to, supply by servo-control means, measurement or detection.The intermediate positions of the moving member 8 can be supplied by aposition sensor 16. The reference electrical characteristic values canthen be associated with the intermediate positions of the moving member8.

Detecting an intermediate position of the moving member 8 in which thereference electrical characteristic is subject to a sudden change can bebased on computing values of the derivative of the reference electricalcharacteristic relative to the position of the moving member 8. Whenthis derivative is plotted as a curve, the curve presents peaks at theintermediate position corresponding to the point at which the movingmember 8 comes into contact with the valve stem 3. The peak or peaks arethe peak derivative value or peak derivative values, respectively. Asused herein, the term “peak derivative value” is the derivative value orderivative values corresponding to the point at which the curve presentspeaks.

The distance between the extreme closed position and the intermediateposition corresponding to the point at which the moving member 8 comesinto contact with the valve stem 3 when the moving member is movingtowards the open position can be deduced. This distance corresponds tothe timing clearance j in the first embodiment.

Likewise, as in the second embodiment, the distance between the extremeopen position and the intermediate position when the moving member ismoving towards the closed position can be deduced. This distancecorresponds to the timing clearance j in the second embodiment.

With reference to the first embodiment, for example, taking a referencecurrent as an example of the reference electrical characteristic, whenthe electromagnetic displacement means causes the moving member 8 tomove from the extreme closed position to the extreme open position, thesudden change in the reference current is representative of a suddenincrease occurring in the force opposing the movement of the movingmember 8. This increase in the opposing force produced by the springwhich moves the valve 1 towards the extreme closed position wherein thespring tends to oppose movement of the valve 1 towards the extreme openposition and the opposing force occurs at the moment when the movingmember 8 comes into contact with the valve stem 3. This sudden change inthe reference current can be associated immediately with an intermediateposition of the moving member 8. Knowing the extreme closed position andthe intermediate position of the moving member 8 at which the referenceelectrical characteristic is subject to a sudden change, a precise valuefor the timing clearance can be easily deduced therefrom.

While the moving member 8 is moved from its extreme closed position toits extreme open position, the electromagnetic means can be controlledinitially to bring the moving member 8 gently up to the intermediateposition corresponding to the point at which the moving member 8 comesinto contact with the valve stem 3 so as to put the moving member 8 intocontact with the valve stem 3. After bringing the moving member 8 up tothe intermediate position corresponding to the point at which the movingmember 8 comes into contact with the valve stem 3, the moving member 8can be accelerated once it is pressing against the valve stem.

While moving the moving member 8 from the extreme open position to theextreme closed position, the electromagnetic means may be controlledfirstly to bring the moving member 8 quickly to the intermediateposition corresponding to the point at which the moving member 8 comesinto contact with the valve stem 3 in order to have rapid closure of thevalve 1, after which the moving member 8 can be brought gently into theextreme closed position in order to limit contact noise between thearmature 12 and the electromagnet 14.

The timing clearance j can be determined periodically. For example, theperiod for determining the timing clearance can include, but is notlimited, one second. Further, the timing clearance can be determinedwhile using different modes of operation of the mechanical device inwhich the timing clearance is determined. This can depend on the speedof the mechanical device and its mode of operation.

With reference to the first and second embodiments as well as the otherenvisaged embodiments referenced above, and for the case in which theembodiments are performed in an engine, the embodiment of the inventionused can depend on the speed of an engine and its mode of operation. Forinstance, since implementation of the first or second embodiment of theinvention does not interfere with normal operation of the actuator 6,they do not generate additional noise, and they can therefore be used atidling speeds as well as at normal operation speeds. Other envisagedembodiments which gives rise to noisier operation of the valve actuator6, can be used when the engine is starting or when the engine isoperating at a speed greater than some predetermined speed, such as 2000revolutions per minute (rpm).

The foregoing description of embodiments of the invention has beenpresented for purposes of illustration and description. It is notintended to be exhaustive or to limit the present invention to theprecise form disclosed, and modifications and variations are possible inlight of the above teachings or may be acquired from practice of thepresent invention. The embodiments were chosen and described in order toexplain the principles of the present invention and its practicalapplication to enable one skilled in the art to utilize the presentinvention in various embodiments and with various modifications as aresuited to the particular use contemplated.

1. A method of determining timing clearance between a valve stem and amoving member using an electromagnetic actuator comprisingelectromagnetic displacement means which comprise electromagnets formoving the moving member between an extreme closed position and anextreme open position, the electromagnets of the electromagneticdisplacement means being controlled by servo-control means on the basisof a reference electrical characteristic, the method comprising:controlling the electromagnetic displacement means to obtain asubstantially constant displacement speed for the moving member betweenthe extreme closed position and the extreme open position; obtainingvalues of the reference electrical characteristic for intermediatepositions of the moving member; and detecting an intermediate positionat which the reference electrical characteristic is subject to a suddenchange.
 2. A method according to claim 1, wherein detecting anintermediate position at which the reference electrical characteristicis subject to a sudden change comprises computing at least onederivative of the reference electrical characteristic relative to atleast one position of the moving member.
 3. A method according to claim2 wherein the reference electrical characteristic is a current.
 4. Amethod according to claim 3, wherein the displacement speed of themoving member is maintained at a speed that is substantially constantover a fraction of the movement of the moving member corresponding to amaximum timing clearance.
 5. A method according to claim 1 wherein thereference electrical characteristic is a current.
 6. A method accordingto claim 1 wherein the reference electrical characteristic is a voltage.7. A method according to claim 1 wherein the valve stem is an enginevalve stem.
 8. A method according to claim 2 wherein the referenceelectrical characteristic is a voltage.
 9. A method according to claim 2wherein the displacement speed of the moving member is maintained at aspeed that is substantially constant over a fraction of the movement ofthe moving member corresponding to a maximum timing clearance.
 10. Amethod according to claim 3 wherein the displacement speed of the movingmember is maintained at a speed that is substantially constant over afraction of the movement of the moving member corresponding to a maximumtiming clearance.
 11. A method of determining timing clearance between avalve stem and a moving member using an electromagnetic actuatorcomprising electromagnets, the actuator being controlled on the basis ofa reference electrical characteristic, the method comprising:controlling an electromagnet to obtain a displacement speed for a movingmember as the moving member moves from one of a closed position and anopen position towards the other one of the open position and the closedposition; obtaining values of a reference electrical characteristic forintermediate positions of the moving member; and detecting anintermediate position at which the reference electrical characteristicis subject to a sudden change.
 12. A method according to claim 11,wherein detecting an intermediate position at which the referenceelectrical characteristic is subject to a sudden change comprisescomputing at least one derivative of the reference electricalcharacteristic relative to at least one position of the moving member.13. A method according to claim 11, wherein detecting an intermediateposition at which the reference electrical characteristic is subject toa sudden change comprises: computing at least one derivative of thereference electrical characteristic relative to at least one position ofthe moving member; and determining the intermediate positioncorresponding to the point of the peak derivative value.
 14. A methodaccording to claim 11 wherein the reference electrical characteristic isa current.
 15. A method according to claim 11 wherein the valve stem isan engine valve stem.
 16. A method according to claim 11 whereincontrolling the electromagnets is performed by a servo-controller.
 17. Amethod according to claim 11 wherein the displacement speed of themoving member is maintained at a speed that is substantially constantover the entire movement of the moving member as the moving member movesfrom one of a closed position or an open position towards the other oneof an open position or a closed position.
 18. A method according toclaim 11 wherein the displacement speed of the moving member ismaintained at a speed that is substantially constant over a fraction ofthe movement of the moving member corresponding to a maximum timingclearance.
 19. A method according to claim 11 wherein obtaining valuesof the reference electrical characteristic for intermediate positions ofthe moving member is performed by a servo-controller.
 20. A methodaccording to claim 11 wherein obtaining values of the referenceelectrical characteristic for intermediate positions of the movingmember is performed by a measuring device.
 21. A method according toclaim 11 wherein obtaining values of the reference electricalcharacteristic for intermediate positions of the moving member isperformed by a detection device.
 22. A method according to claim 11,further comprising deducing a timing clearance.
 23. A method accordingto claim 22, wherein deducing the timing clearance is based on theclosed position and the intermediate position.
 24. A method according toclaim 22, wherein deducing the timing clearance is based on the openposition and the intermediate position.
 25. A method according to claim12 wherein the reference electrical characteristic is a current.
 26. Amethod according to claim 12 wherein the displacement speed of themoving member is maintained at a speed that is substantially constantover the entire movement of the moving member as the moving member movesfrom one of a closed position or an open position towards the other oneof an open position or a closed position.
 27. A method according toclaim 12 wherein the displacement speed of the moving member ismaintained at a speed that is substantially constant over a fraction ofthe movement of the moving member corresponding to a maximum timingclearance.